1. Technical Field
The present invention relates, generally, to extension tables having integral slide assemblies for supporting at least one supplemental interior table-top leaf when the table is extended, and, more particularly, to tableslide assembly elements made from materials which contribute to decreased production costs and increased performance characteristics.
2. Description of the Background Art and Technical Problems
It is generally known to provide slide assemblies for extension tables to permit the ends of a table to be extended or moved apart so that additional leaves may be inserted between the extended ends. See, Dobbratz U.S. Pat. No. 3,927,918, issued Dec. 23, 1975, the disclosure of which is hereby incorporated by reference and relied upon.
In a typical tableslide assembly, one slide member is secured to the underside of one end of an extension table while an adjacent slide member is secured to the opposite end, the adjacent slide members having respective oppositely disposed bearing surfaces. As the table ends are moved apart or urged together, those bearing surfaces of adjacent slide members maintain relative sliding engagement.
Each slide member includes a lengthwise channel formed in the bearing surface thereof. A guide block is disposed between adjacent slide members. The guide block advantageously comprises a pair of oppositely disposed projections for receipt within the respective channels of the slide members. The projections are configured to generally correspond to the geometry of the channel, for example in a male/female relationship. The dimensions of the projections are preferably slightly less than the corresponding dimensions of the channel to allow the former to freely slide within the latter. More specifically, a range of acceptable dimensions, or a tolerance, is associated with each guide block and channel, resulting in a loose fit configuration, within predetermined boundaries, for each projection/channel combination.
During the design phase, an optimum magnitude is assigned to each dimension (i.e., length, width, height, taper, thickness, radius, for example) associated with respective tableside elements. The maximum amount of relative slop which can be tolerated between a projection and a channel is then determined, and a range of allowable deviation from the optimum value is assigned to each dimension. This range, or tolerance, constitutes the range of acceptable dimensional integrity. Individual elements having dimensions outside the tolerance are either reworked or disgarded.
When the extension table is in the extended position, the assembly, and particularly the guide block, must bear the substantial load attributed to the weight of the tabletop insert and any objects placed thereupon. Thus, the block should be made from a material which possesses sufficient strength, yet at the same time is cost effective to manufacture. Similarly, the slide members should be made from a material having good strength and manufacturability characteristics.
To prevent the mid-portion of an extended table from sagging when objects, for example dishes or books, are placed thereon, it is desirable to incorporate a camber into the tableslide design. That is, the tableslide assembly elements are configured such that, in the unloaded but extended position, the slide members are inclined upwardly towards the middle of the table. When the tabletop leaf is put in place, the upward arching of the tableslide assembly is loaded downwardly and the table assumes a horizontal position. The extent to which sagging of the mid portion of the table can be compensated for is limited by the degree of camber actually or potentially embodied in the tableslide assembly. The degree or slope of the camber, however, is determined by the dimensions of the respective tableslide assembly elements. As such, to the extent the dimensions of any particular element approach or exceed the desired tolerance, a corresponding reduction in camber results. Thus, maximizing the extent to which table sag can be compensated for involves minimizing the amount of camber which is consumed by excessive dimensional deviations (i.e., slop).
An important consideration in the selection of slide member and guide block materials is the ease with which dimensional integrity may be maintained during manufacture. Wooden tableslide members, used in conjunction with wooden guide blocks, are generally well known. See, for example, Carter and Mets Reissue U.S. Pat. No. 4,317, reissued Apr. 4, 1871 (reissue of U.S. Pat. No. 44,073, issued Sept. 6, 1864). Wooden tableslide members are easy to manufacture and relatively inexpensive. However, wooden slide members tend to warp and thus do not maintain good dimensional integrity during temperature and humidity changes, especially over long periods of time.
Alternatively, steel and aluminum slide members, in conjunction with plastic guide blocks, have been suggested. See U.S. Pat. No. 3,927,918. These materials exhibit good dimensional integrity despite temperature and humidity changes. On the other hand, the materials are generally more expensive and more difficult to fabricate than wood. Steel slide members have an additional disadvantage inasmuch as they are subject to corrosion.
Another important design consideration involves the ease with which an extension table may be pulled apart or urged together. Guide blocks made from high lubricity plastics having a low coefficient of sliding friction have been suggested for use in conjunction with aluminum slide members. See U.S. Pat. No. 3,927,918. Also as discussed in the '918 patent, the plastic guide blocks include thin flat extensions, or fins, adapted for disposition between the mating surfaces of the aluminum slides to prevent contact between adjacent slide members, thus reducing friction and noise. These fins, however, tend to warp during cooling if injection molded, are difficult to eject from an injection press, and can render a tableslide inoperable if a fin breaks during use.